The present invention generally relates to a braking apparatus and method for use with a moving vehicle. The present invention particularly relates to a braking apparatus and method which slows down a moving vehicle by neutralizing an associated hydrostatic transmission prior to actuating a conventional brake system of the vehicle.
Many earth moving machines, such as front end loaders, employ a hydrostatic transmission for propulsion. However, it is also known that operating the hydrostatic transmission in a certain manner can assist in braking or stopping the machine. One such method incorporates an "inching valve" in fluid communication with the hydrostatic transmission. When activated the "inching valve" bleeds off a volume of hydrostatic fluid from the hydrostatic transmission, which in turn causes a temporary reduction in a hydrostatic control pressure of the system. This decrease in control pressure causes an appropriate controller component to "destroke" or neutralize the hydrostatic transmission. A hydrostatic transmission in a "destroked" or neutralized mode delivers a reduced amount of driving force to the vehicles wheels, and thus assists in braking or stopping the vehicle.
One prior art approach to coordinate an "inching valve's" function (and therefore a "destroking" of the hydrostatic transmission) with a conventional braking system of a vehicle has been to mechanically link the "inching valve" to a separate braking element, such as a piston in the master cylinder of a hydraulic braking system. This mechanical linkage allows the "inching valve" to become activated upon actuation of the braking element. However, this approach has the disadvantage of requiring precise tolerances between the parts mechanically interposed between the "inching valve" and the braking element to ensure that the destroking function is initiated before a set of brake pads or shoes engage a disk or drum of the braking system. If the timing is not appropriately set by the mechanical linkage, for example if the "destroking" function occurs at a point in time slightly after actuation of the braking system, the hydrostatic transmission will be operating to propel the vehicle forward at the same time the braking system is attempting to slow down the vehicle. The situation results in excessive brake pad wear and deterioration. An additional disadvantage of utilizing a mechanically linked "inching valve" is that it requires additional parts to link the elements. These additional parts add unnecessary bulk and cost to the braking apparatus of the vehicle.
Therefore, in light of the above discussion, it is apparent that an apparatus and method for coordinating the destroking of a hydrostatic transmission with a conventional braking system is desirable. The present invention provides such an apparatus in the form of an inching valve integrated with a braking element, such as a piston in a hydraulic braking system. One advantage in the present invention is that the timing of the destroking (or neutralization) function is not dependent upon the tolerances of mechanically interposed parts. Moreover, an inching valve integrated with a braking element eliminates the need for mechanical linking elements which add to the cost and bulk of a braking system.